ZoneIngresses are not garbage collected

[nicoche]

What happened?

Kuma version 2.5

It seems that disconnected ZoneIngresses are not being cleaned up. Here is an example of a ZoneIngress disconnected since a few weeks:

Here is an example ZoneIngressInsight:

{
  "subscriptions": [
    {
      "id": "fb25e856-02d2-4508-b6c9-6cabebe54e46",
      "controlPlaneInstanceId": "cp-v2-fra1-65ccf5cbfd-xns5l-c1af",
      "connectTime": "2023-12-08T08:01:48.354625590Z",
      "disconnectTime": "2023-12-08T09:01:49.621651397Z",
      "status": {
        "lastUpdateTime": "2023-12-08T08:01:49.621132910Z",
        "total": {
          "responsesSent": "2",
          "responsesAcknowledged": "4"
        },
        "cds": {
          "responsesSent": "1",
          "responsesAcknowledged": "2"
        },
        "eds": {},
        "lds": {
          "responsesSent": "1",
          "responsesAcknowledged": "2"
        },
        "rds": {}
      },
      "version": {
        "kumaDp": {
          "version": "0.0.0-preview.v0e49166df",
          "gitTag": "none",
          "gitCommit": "0e49166dfc0e08392bd3259515633eee6b0e5c4c",
          "buildDate": "2023-11-24T21:40:10Z",
          "kumaCpCompatible": true
        },
        "envoy": {
          "version": "1.27.0",
          "build": "7bba38b743bb3bca22dffb4a21c38ccc155fbef8/1.27.0/Modified/RELEASE/BoringSSL",
          "kumaDpCompatible": true
        }
      },
      "generation": 24
    },
    {
      "id": "3499a1e7-c545-4189-8f8b-61f8aa66538f",
      "controlPlaneInstanceId": "cp-v2-fra1-65ccf5cbfd-b8xcq-f486",
      "connectTime": "2023-12-08T09:01:50.054905886Z",
      "disconnectTime": "2023-12-08T09:07:41.546965959Z",
      "status": {
        "lastUpdateTime": "2023-12-08T09:01:51.277599407Z",
        "total": {
          "responsesSent": "2",
          "responsesAcknowledged": "4"
        },
        "cds": {
          "responsesSent": "1",
          "responsesAcknowledged": "2"
        },
        "eds": {},
        "lds": {
          "responsesSent": "1",
          "responsesAcknowledged": "2"
        },
        "rds": {}
      },
      "version": {
        "kumaDp": {
          "version": "0.0.0-preview.v0e49166df",
          "gitTag": "none",
          "gitCommit": "0e49166dfc0e08392bd3259515633eee6b0e5c4c",
          "buildDate": "2023-11-24T21:40:10Z",
          "kumaCpCompatible": true
        },
        "envoy": {
          "version": "1.27.0",
          "build": "7bba38b743bb3bca22dffb4a21c38ccc155fbef8/1.27.0/Modified/RELEASE/BoringSSL",
          "kumaDpCompatible": true
        }
      },
      "generation": 2
    }
  ]
}

With

creation_time     | 2023-11-22 20:18:03.630251
modification_time | 2023-12-08 09:07:41.548026

More info: https://kuma-mesh.slack.com/archives/CN2GN4HE1/p1707322051004629